Transformer less Inverter for Single-Phase Photovoltaic Systems

When no transformer is used in a grid- connected photovoltaic (PV) system, a galvanic connection between the grid and PV array exists. In these conditions, dangerous leakage currents (common-mode currents) can appear through the stray capacitance between the PV array and the ground. In order to avoid these leakage currents, different inverter topologies that generate no varying common-mode voltages, such as the half-bridge and the bipolar pulse width modulation (PWM) full-bridge topologies, have been proposed. The bipolar PWM full bridge requires a lower input voltage but exhibits a low efficiency. This paper proposes a new high-efficiency topology that generates no varying common-mode voltage and requires the same low-input voltage as the bipolar PWM full bridge.